As disclosed in Patent Document 1, there is a conventional cylindrical battery that includes a battery case having a cylindrical shape, and an electrode group having a columnar shape and accommodated in the battery case. In the electrode group, belt-shaped positive and negative electrode plates are spirally wound with a belt-shaped separator being interposed therebetween. In order to enhance capacity, this cylindrical battery is configured such that the battery case accommodates the columnar electrode group such that the battery case is almost solid inside. The battery case is in surface contact with the negative electrode located on the outermost periphery of the cylindrical electrode group, so that current is collected from the negative electrode.
The applicant of the present invention has been developing a cylindrical battery of low capacity suitable for a purpose of use, although cylindrical batteries have been enhanced in capacity in recent years. More specifically, the applicant has been considering reduction in size of the electrode group relative to the battery case by reduction in outer diameter of the columnar electrode group accommodated in the battery case, for example.
However, when the electrode group is reduced in size relatively to the battery case, the electrode group cannot be sufficiently in contact with the battery case and it is difficult to collect current from the negative electrode.